NCBC-333 - NCBC-310: Amendment #3 - reference cleanup when SocketPool is disposed

Change-Id: Ieba7b17f650f413edea4c29aec3cde39fac7324a
Reviewed-on: http://review.couchbase.org/30294
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>